What Is a Lactose Tolerance Test?

Overview

A lactose tolerance test is a test that
measures how well your body can process lactose, a type of sugar found in dairy
products. Normally the body is able to process milk and other dairy products
thanks to an enzyme in the intestines called lactase, which breaks lactose down
during digestion.

However, some people have levels of lactase
that are lower than normal. For these people, instead of breaking down the milk
sugar (lactose), the lactose will persist in the intestines and ferment. This
inability to digest lactose is referred to as lactose intolerance.

Types of Tests

There are three kinds of tests that can be
used to check lactose intolerance:

Hydrogen Breath Test

This test is the most common. During this
test, your doctor will instruct you to drink a liquid solution containing
lactose, and will then have you breathe into a balloon-like instrument at set
intervals to determine how much hydrogen there is in your breath. The more
hydrogen you exhale, the more likely it is that your body is unable to process
lactose.

Lactose Tolerance Test

Like the hydrogen breath test, this test also
requires you to drink a liquid with lactose. After two hours, your doctor will
take a blood sample to measure how much glucose is in your blood. If your blood
glucose level does not rise, this means that your body is not digesting or
absorbing lactose.

Stool Acidity Test

This test is usually performed on infants or
small children, as they are not eligible for other tests. A physician will take
a stool sample to see if lactose is breaking down properly in your system.
Fermenting lactose in the intestines (a sign of lactose intolerance) creates
lactic acid, which can be detected in stool.

These tests may be performed in your
physician’s office or in an outpatient laboratory.

When Would Your Doctor Recommend a Lactose Tolerance
Test?

Your physician may recommend this test if you
have symptoms of lactose intolerance. Signs of lactose intolerance include
feeling nauseated or getting cramps shortly after consuming dairy foods.
Diarrhea, gas, and bloating after eating foods with lactose are also common
symptoms.

According to the National
Digestive Diseases Information Clearing House (NDDIC), lactose intolerance occurs more often in older adults and babies
who are born prematurely. If your doctor thinks you are lactose intolerant, he
or she may ask you to eliminate all dairy products from your diet for a short
time to see if symptoms improve.

How Do You Prepare for a Lactose Tolerance Test?

To prepare for the test, it is a good idea to
ask your doctor about which test you will be taking, and to ask about any
dietary restrictions. Your physician may ask that you not eat or drink for
eight hours before the test. Your physician may also restrict your exercise.

Make sure your provider knows about any other
conditions you may have and any medications you are currently taking. Some
medications and foods can interfere with test results. Smoking may also affect
test results. If you are a smoker, ask your doctor if you should abstain from
tobacco prior to taking the test.

What Happens During a Lactose Tolerance Test?

Hydrogen Breath Test

Before the test, your doctor will ask you to
breath into a balloon-like device to obtain a baseline, or typical reading of
how much hydrogen is in your breath after fasting. Next, your doctor will have
you drink a liquid that contains lactose and water. As your body digests the
lactose, your doctor will ask you to breathe into the balloon-like device
several times over a few hours to measure how much hydrogen is in your breath.
This is typically done in 15-minute intervals for approximately two to three
hours. Increased levels of hydrogen in the breath indicate that the body is not
properly breaking down or absorbing lactose.

Lactose Tolerance Test

For this test, your doctor will take a
fasting blood sample to obtain a baseline, or typical, reading of how much
glucose is in your blood. Then, like the hydrogen breath test, your doctor will
have you drink a liquid with lactose. As your body digests the lactose, it
should break the lactose down into a simpler sugar called glucose. Your doctor
will take blood samples several times over a few hours to measure how much
glucose is in your blood.

Stool Acidity Test

This test is primarily for infants and young
children. In this test, the doctor will have the infant or child drink a liquid
with lactose. After waiting, the physician will take a stool sample. Normally,
a stool is not acidic. However, if the body cannot break down lactose, lactic
acid and other acids will appear in the stool.

Interpreting Your Test Results

Your doctor will discuss the results with you
after the test. Remember, some results vary by doctor’s office and clinic.

Hydrogen Breath Test

A hydrogen breath test result that shows a
rise in hydrogen of more than 12 parts per
million over your original fasting test indicates
lactose intolerance.

Lactose Tolerance Test

You may be lactose intolerant if blood
glucose levels raise less than 20 mg/dL (milligrams per deciliter) within two
hours of drinking the lactose solution, according to the U.S. National Library
of Medicine.

Be sure to discuss what these results mean
with your doctor and how you can manage your condition.

This feature is for informational purposes only and should not be used to replace the care and information received from your health care provider. Please consult a health care professional with any health concerns you may have.